Object direction control method and apparatus

ABSTRACT

A direction control method and apparatus control the direction of a traveling object on a monitor, for example, in a video game device. An object having, for example, two elements to be directionally controlled with each of the elements being controllable in a rotational direction is displayed along with its background in a traveling state on a monitor. The object includes, for example, a war tank (31) used in a war game of a game device. The two elements to be directionally controlled includes a body (32) and a sight (33) of the tank (31). A target angle θ is designated by a single direction input unit 20(A) for the vehicle body (32) and the sight (33). The rotational direction of the sight (33) is controlled on the basis of the target angle θ. The rotational angle of the vehicle body (32) is controlled following the sight (33) on the basis of the traveling velocity of the tank (31) and the rotational angle Ya of the sight (33).

TECHNICAL FILED

The present invention relates to a direction control method andapparatus for controlling the direction of an object on a monitor ofeach of a home and an arcade video game device, and more particularly toa direction control method and apparatus which is applied to a gamedevice which has an input unit by which the player designates thedirection of an object.

BACKGROUND ART

Video game devices are classified roughly into home and arcade ones inaccordance with use. The home video game devices generally have a gamedevice body and a controller such as a joy pad each with the game devicebody being connected, for example, to a home video monitor. When acassette ROM is inserted into the game device body and a start button isdepressed, a game program stored in the cassette ROM is read by the gamedevice body. When the player manipulates the controller to give anoperational signal to the game device body, the game program starts upin the game device body to produce a video signal and an audio signal,which are delivered to the video monitor and displayed as an image andoutputted as a sound, respectively.

Many arcade video game devices have a cockpit-like housing in which thegame device body containing game programs and a large display screen areprovided. A manipulation seat on which the player sits is providedfacing the display. The player views a game screen while playing thegame by operating the control unit such as a steering-type input unitprovided at the player's seat.

The direction of a traveler or vehicle (a travelable character)displayed on the video monitor or display is controlled by the player'soperation of the joy pad and/or steering-type input unit in the videogame device. There are various travelers. Some travelers are required tobe controlled in two directions as the case may be. For example, somegames have a war tank as a traveler. In this case, the two directionsare the traveling direction of the tank itself and the direction ofsight of a canon mounted on the tank. When the directions of the tank,as well as the sight of the canon, are controlled, two steering elementsare required; a regular steering element and a second steering elementfor sight control. Alternatively, both a direction key and a steeringelement are provided and operated.

In many cases, the home video game devices have only a joy pad as acontrol unit. Thus, in many cases, the joy pad and a steering elementare used in combination. When the steering element is manipulated whiledepressing a button switch on the joy pad, the direction of canon sightis controlled, while when only the steering element is manipulated, thedirection of the tank itself is controlled.

However, when the two devices are provided separately to control the twodirections of the same traveler, the whole control unit of the gamedevice becomes large-scale and complicated. Since the player is requiredto operate the two devices simultaneously or in parallel, themanipulation itself becomes complicated and the direction control whichthe player is intended to provide cannot be provided timely as the casemay be, so much so that the complicated direction control can reduce theplayer's interest in the game itself.

DISCLOSURE OF THE INVENTION

It is a main object of the present invention to provide a directioncontrol method and apparatus which simplifies the player's operation fordirection control in a game which requires control of a plurality ofdirections in the same traveler.

Another main object of the present invention is to provide a directioncontrol method and apparatus which simplifies the player's operation fordirection control in a game which requires control of a plurality ofdirections in the same traveler, and avoiding the control unit of thegame device being large-scale and complicated.

One of specified objects of the present invention is to provide adirection control method and apparatus which when traveling or moving,the direction of a traveler or vehicle in a game such as a war tank andthe sight direction of a canon mounted on the tank is controlled inparallel, the invention simplifies the player's operation for directioncontrol.

In order to achieve the above objects, the present invention provides anobject direction control method of displaying on a monitor an objecthaving a plurality of direction control elements each of which iscontrollable in a rotational direction, along with a background in amoving state, comprising the steps of designating a target angle for theplurality of direction control elements, controlling the rotationalangle of any particular one of the plurality of direction controlelements on the basis of the target angle, and controlling therotational angle(s) of the remaining direction control element(s) so asto follow up the particular direction control element.

The number of direction control elements is two. The object comprises,for example, a war tank used in a tank game of a game device, and thetwo direction elements to be controlled comprise the body and sight ofthe tank. Preferably, the particular element to be directionallycontrolled comprises the sight, and the remaining element to bedirectionally controlled comprises the body of the tank.

For example, the particular element to be directionally controlled isrotated at a given velocity in accordance with the target angle.Preferably, a new rotational angle Ya of the particular element to bedirectionally controlled is given by

    Ya=Yb+Ka·θ

where θ is the target angle, Yb is the current rotational angle of theparticular element to be directionally controlled, and Ka is a constant.

For example, the remaining element(s) to be directionally controlled arerotated depending on the moving velocity of the object and therotational angle of the particular element to be directionallycontrolled. Preferably, a new rotational angle Za of the remainingelement(s) to be directionally controlled is given by

    Zo=Ya

    Za=Zb+Kb·V·(Zo-Zb)

where Zo is the target rotational angle of the remaining element(s) tobe directionally controlled, Ya is the rotational angle of theparticular element to be directionally controlled, Zb is the currentrotational angle of the remaining element(s) to be directionallycontrolled, Kb is a constant, and V is the moving velocity of theobject.

Further, preferably, the given velocity of rotation of the particularelement to be directionally controlled is slightly higher than themaximum rotational follow-up velocity of the remaining element(s)directionally controlled.

The present invention provides an object direction control apparatus fordisplaying on a monitor an object having a plurality of directioncontrol elements each of which is controllable in a rotationaldirection, along with a background in a moving state, comprising targetangle designating means for designating a target angle for the pluralityof direction control elements, first direction control means forcontrolling the rotational direction of any particular one of theplurality of direction control elements on the basis of the targetangle, and second direction control means for controlling the rotationaldirections of the remaining direction control element(s) by following upthe particular direction control element.

For example, the number of direction control elements is two. The objectis a war tank used in a tank game in a game device. The two elements tobe directionally controlled comprise the body and sight of the tank. Thetarget angle designating means comprises a single direction input unitfor manually inputting direction data on a target angle.

Thus, for example, the rotational direction of the sight in the tankgame is controlled by input information from a single direction inputunit and the rotational direction of the vehicle is controlled followingup the canon sight. Thus, the control unit is required only to have, forexample, a sight steering element (direction input unit). Thus, theoperation is simplified and the player has an increased margin forsufficiently enjoying a game played using the present invention. Withthe present invention, the structure of the control unit is simplified,and the whole device is reduced in size and simplified.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a game device to whichan object direction control method and apparatus according to thepresent invention is applied;

FIG. 2 schematically shows a war tank as an object;

FIG. 3 is a block diagram of an electric system of the embodiment;

FIG. 4 is a block diagram of an electric system which includes afunctional block structure of a central processing unit and itsperipheral circuits;

FIG. 5 is a flow chart which indicates the outline of a process whichmainly provides the direction control of the central processing unit;

FIG.6 illustrates the relationship between the traveling velocity of atank, and the sight and the rotational velocity of the tank body;

FIGS. 7A-7C illustrate the positional relationship between a virtualcamera and a tank;

FIG. 8 illustrates the visual field of a virtual camera and thetravelling direction of a tank;

FIG. 9 illustrates a video monitor screen;

FIG. 10 illustrates vectors indicative of the rotational situation ofthe sight and tank body in time series when the tank travels at lowvelocity; and

FIG. 11 illustrates vectors indicative of the rotational situation ofthe canon sight and tank body in time series when the tank travels atthe highest velocity.

PREFERRED EMBODIMENTS OF THE INVENTION

One embodiment of the present invention will be described next withreference to the drawings.

FIG. 1 shows the appearance of an arcade video game device of thisembodiment. The game device includes a functionally mounted objectdirection control method and apparatus according to the presentinvention.

The game device of FIG. 1 has a housing 1 which forms a cockpit. Thehousing 1 has a bottom 1A and a front 1B which continues to one end ofthe base 1A so as to be perpendicular to the base. The bottom 1A has aplayer's manipulation seat 2 on which the player sits to manipulate thegame device. The front 1B has a game device body 10 therein. Provided atthe player's seat 2 are a control unit 20 which includes a steeringelement 20A, an accelerator 20B, and a view change switch 20C; a videomonitor 30 and a speaker 40 on the upper front.

The game device handles a tank game. The steering element 20A is theonly control unit which gives direction data to the game device. Thetank game handles the tank as a traveling or moving display object(vehicle). The tank 31 can be expressed schematically, as shown in FIG.2, and has a body 32 and a canon sight 33.

The electric block diagram of the game device is shown in FIG. 3. Thegame device body 10 includes a central processing unit (CPU) 101, anauxiliary processor 102, a program/data ROM 103, a data RAM 104, abackup RAM 105, an input interface 106, a dip switch 107, a sound device108, a power amplifier 109, a polygon parameter memory 110, a coordinateconverter 111 called a geometrizer, a polygon data memory 112, a polygonpaint unit 113 called a rendering unit, and a frame memory 114.

The central processing unit (CPU) 101 is connected through a bus line tothe auxiliary processor 102, program/data ROM 103, data RAM 104, backupRAM 105, input interface 106, sound unit 108, and polygon parametermemory 110. The input interface 106 is connected to the control unit 20and the dip switch 107. The CPU 101 reads data on a game programcontained beforehand in the program/data ROM 103 in cooperation with theauxiliary processor 102 to execute the program. The game programcontains the control of the position, direction and angle of a tank asan object displayed on the video monitor 30 and control of the positionand angle of a virtual camera which determines the visual field of thedisplay screen. The outline of the control is shown in FIG. 5.

The virtual camera can be compared to a regular camera in terms of aviewpoint and an image angle used when computer graphics are delineated.The setting of the virtual camera is performed by designating theposition, optical axis direction (the direction of the lens), an imageangle (zoom-wide), and a twist (a rotational angle around the opticalaxis). In other words, the virtual camera is a virtually set viewpoint.The virtual camera is understood as a virtual visual field directiondetermining means for determining the visual field direction of an imagedisplayed on the video monitor. An object (figure) which has beenmodeling-converted from a body coordinate system inherent in the figureto a world coordinate system which defines the disposition of the figure(object) in a three-dimensional space is converted in visual field to avisual field coordinate system defined by (the position and angle of)the virtual camera and the resulting object figure is then displayed onthe monitor 30.

The sound device 108 is connected through the power amplifier 109 to thespeaker 40. An acoustic signal produced by the sound device 108 isamplified by the amplifier 109 and delivered to the speaker 40.

A read terminal of the polygon parameter memory 110 is connected to acoordinate conversion unit 111 to which polygon parameters in the memory110 are delivered. The coordinate conversion unit 111 is connected to apolygon data memory 112 so as to receive polygon data from the memory112. The coordinate converter 111 converts three-dimensional polygoncoordinate values to be displayed in two-dimensional perspectivecoordinate values on the basis of given polygon parameters and polygondata. The output of the coordinate converter 111 is connected to thepolygon paint unit 113 such that the polygon data which has beenconverted so as to have the perspective coordinates is delivered to thepolygon paint unit 113, which paints received polygons with texture datastored in the frame memory 114 to form image data. The output of thepolygon paint unit 113 is connected to the video monitor 30 on which theimage data formed by the paint unit 113 is displayed.

An accelerator 20B of the control unit 20 outputs an electric signalindicative of an accelerator opening A which is reflected by a travelingvelocity V of the object on the video monitor 30 in response to theplayer's operation. Similarly, the steering element 20A outputs anelectric signal indicative of a direction θ in which the actions of theobject are reflected. The steering element 20A composes object angledesignating means in the present invention. The view change switch 20Cis a switch with which the player designates the position of the virtualcamera which determines the visual field of an image displayed on thevideo monitor 30.

FIG. 4 shows a block diagram of a part of the functions of the CPU 101and its peripheral circuits (surrounded by a dot-dashed line) of FIG. 3.The CPU 101 and its peripheral circuit performs the processing of FIG. 5to be described later to functionally realize a player position anglecalculation system 121, a camera position angle calculation system 131,and an n-object position angle calculation system. The player positionangle calculation system 121 functionally includes a traveler or vehiclevelocity calculation means 122, sight direction control means 123, and atraveler or vehicle follow-up data creation means 124.

The processing of FIG. 5 which the CPU 101 performs in cooperation withthe auxiliary processor 102 will be described next. This process isperformed, for example, on a timer interrupt basis at predeterminedintervals of Δt.

First, an accelerator opening A from the accelerator 20B is read (step201). From an opening degree A of the accelerator, a traveling velocityV of the tank 31 as an object is calculated on the basis, for example,of table lookup (step 202).

A signal indicative of the steering angle θ of the steering element 20Ais read (step 203), and a sight angle Ya used to control the sightdirection is calculated on the basis of the steering angle θ as follows(step 204):

    Ya=Yb+Ka·θ                                  (1)

where Yb is the current sight angle 33, Ka is a constant to rotate thesight 33 at a given velocity α, which will be described with referenceto FIG. 5. As shown in FIG. 6, set beforehand in the program/data ROM103 is a table which has beforehand stored data on the relationshipexpressed by a straight line δ between the traveling velocity V of thetank 31 (horizontal axis) and the rotational velocity Vr of the tank 31or its body 32 (vertical axis). As will be described later, the linearline δ is used to determine a rotational velocity Vr from a traveling ormoving velocity V and defines a proportional state from the travelingmoving velocity V=0 (at this time, the rotational velocity Vr=0) to thehighest traveling velocity V=Vmax (at this time, the highest rotationalvelocity Vr=Vrmax). In FIG. 6, the predetermined velocity α is alwaysset at a predetermined velocity slightly higher than the highestrotational velocity Vrmax irrespective of the traveling velocity V.

As described above, when a sight angle Ya is calculated which rotates atthe predetermined velocity by an angle depending on the steering angleθ, the current value Yb is updated with the new calculated value Ya forthe next time operation (step 205).

The CPU 101 then sets the calculated sight angle Ya as a target rotationdirection Zo of the tank 31 to create object follow-up data (step 206)and calculates the rotational angle Za of the tank 31 (step 207) asfollows:

    Za=Zb+Kb·V·(Zo-Zb)                       (2)

where V is the traveling velocity of the tank 31, Zb is the currenttraveling direction of the tank, and Kb=γ/Vmax (constant) (0<γ<1) whereVmax is the highest traveling velocity of the tank 31.

The second term "Kb·V" of expression (2) is expressed by the straightline δ (=Kb·V) of FIG. 5. When the traveling velocity V of the tank 31is low, for example, V=Vs, the rotational velocity Vr becomes a lowvelocity Vr=Vrs in accordance with the straight line δ. When thetraveling velocity V of the tank 31 is medium, for example, Vv=Vmd, therotational velocity Vr also becomes a medium velocity Vr=Vrmd. When thetraveling velocity V of the tank 31 is the highest one V=Vmax, therotational velocity Vr becomes the highest velocity Vrmax, which isslightly lower than the rotational velocity a of the sight 32.

As described above, when a new rotational angle Za of the tank 31 isdetermined, this rotational angle Za is set in place of the currentrotational angle Zb for creation of the next-time follow-up data (step208).

The CPU 101 then reads information about the operation of the viewchange switch 20C designed by the player other than the acceleratoropening A, and the steering angle θ (step 209).

Among the information about the operation, already processed switchinformation from the view change switch 20C and the steering angle θ ofthe steering element 20A, as described above, is used to calculate theposition and angle of the virtual camera. More specifically, the cameraposition and angle (direction) optimal for display on the video monitor30 are calculated on the basis of the calculated latest sight angle Ya,vehicle body rotational angle Za and the information about the operation(step 210). The position and direction of the camera are conditionswhich define an image displayed on the monitor in the world of a gameconstructed three-dimensionally. Switch information from the view changeswitch 20C changes the positional relationship between the tank 31 andthe camera. More specifically, it changes the position (distance) andangle of elevation of the tank 31 relative to the camera.

For example, it is determined whether a camera 130 is disposed directlyabove the tank 31, as shown in FIG. 7A, whether the camera 130 isdisposed obliquely above and behind the tank 31, as shown in FIG. 7B, orwhether the camera 130 is disposed high in the sky behind the tank 31,as shown in FIG. 7C. In the case of the positional relationship of FIG.7A, the image pick up range PR of the camera 130 is present in thetravel direction of the tank 31, which aligns with the center line ofthe image pick-up range PR of the camera 130, as shown in FIG. 8. An eye(the left and right directions of the viewpoint) is determined, whichrotates around an axis normal to the ground surface, in accordance withthe angle Ya of the sight 33 determined on the basis of the steeringangle. An image in front of the tank 31 in the eye direction defined bythe position and angle of the camera, thus determined, is displayed onthe video monitor 30 (FIG. 9).

The position and angle of an object optimal for display on the videomonitor 30 are selected on the basis of the latest sight angle Ya,vehicle body rotational angle Za and other operation information (step211). Since a plurality of (n) objects such as an enemy tank, a player'stank, a background and the sky is prepared beforehand, appropriateobjects which fall in the visual field of the camera are selected fromamong the n objects.

Polygon parameters used for display on the basis of the various resultsof the calculations obtained as mentioned above, are calculated. Thepolygon parameters are delivered along with information about thedesignation of polygons used for display to the polygon parameter memory110 (steps 212, 213). That is, information about coordinate conversion(movement, rotation, enlargement, reduction, etc.) anddisplay/non-display of the respective objects is stored in the polygonparameter memory 110.

The processing of FIG. 5 composes first and second direction controlmeans of the present invention. Steps 201-208 of the processingfunctionally compose the player position angle calculation system 121.The steps 201 and 202 correspond to the vehicle velocity calculationmeans 122. Steps 203-205 correspond to the sight direction control means123. Steps 206-208 corresponds to the vehicle follow-up data creationmeans 124. Steps 210 and 211 functionally realize the essential portionsof the camera position angle calculation system 131 and the essentialportion of the n-object position angle calculation system, respectively.

The coordinate converter (geometrizer) 111 reads information stored inthe polygon parameter memory 110 and performs coordinate conversioninvolving a matrix operation on objects stored in the polygon datamemory 112 on the basis of the read information to thereby providedisplay data, which is then delivered to the polygon paint unit 113where the display data is coated with texture data stored in the framememory 114. The display data expressed very realistically by thattexture mapping is then delivered to the video monitor 30 and variousobjects including the tank 31 are displayed in the background BK on areal-time basis, as shown in FIG. 9.

Subsequently, an illustrative specified operation of the device will bedescribed next.

Assume now that the step-down quantity of the accelerator 20B by theplayer is small and the accelerator opening A is small. The acceleratoropening A is delivered to the CPU 101 through the input interface 106.The CPU 101 calculates the traveling velocity V of the tank 31 on thebasis of the accelerator opening A. If the steering element 20A has notbeen operated, a polygon parameter corresponding to the travelingvelocity V is calculated. Thus, the tank 31 and its background BK appearto change at a slow velocity V relative to each other on the displayscreen of the monitor 30 and the tank 31 appears to travel at therelative velocity V.

Assume now that during the travel of the tank the player tries to turnthe steering element 20A through a desired angle θ (in this example, 90degrees). This steering angle θ is read through the input interface 106by the CPU 101, which calculates a sight angle Ya through which thesight 33 is rotated in the steering direction of the steering element inunits of a small increment of the changing steering angle of the momentat the given velocity a (FIG. 6), using the expression (1). The sightangle Ya is handled as a target rotational angle Zo and a rotationalangle Za is calculated which rotates the tank body 32 while followingthe sight 33. In this calculation, the rotational angle Za is calculatedas an angle smaller by a coefficient "Kb·V" of the expression (2) thanthe sight angle Ya. In this case, since the traveling velocity V is low,the value of the coefficient "Kb·V" is small, so that data on therotational angle Za of the vehicle body 32 is delayed greatly comparedto the sight angle Ya.

This situation is schematically shown in FIGS. 10 (1)-(7). Morespecifically, as the time elapses from t1 to t7, the sight 33 changes,for example, in order of 0 degrees (initially, time t1), 30 degrees(time t2), 60 degrees (time t3), and 90 degrees (after time t4) incorrespondence to the respective time-dependent changes of the steeringangle θ through 90 degrees. Parallel with this, the rotation (direction)of the vehicle body 32 changes or is gradually delayed relative to thesight angle, for example, in order of 0 degrees (time t1) (in this case,the rotational angles of the vehicle body and sight angle are the same(0 degrees)), 15 degrees (time t2), 30 degrees (time t3), 45 degrees(time t4), 60 degrees (time t5), 75 degrees (time t6), and 90 degrees(time t7). That is, when the tank 31 travels at a low velocity, thequantity of delay is comparatively large.

In contrast, assume now that a step-down quantity of the accelerator 20Bapplied by the player is large, for example, the accelerator opening Ais maximum. The accelerator opening A is read by the CPU 101, asdescribed above, and the traveling velocity V=Vmax of the tank 31 iscalculated. Assume now that the steering element 20A has not beenoperated. In this case, polygon parameters corresponding to thetraveling velocity Vmax is calculated, so that the tank 31 and thebackground BK appear to change at high velocity V=Vmax relative to eachother on the display screen of the monitor 30, and the tank 31 appearsto move at the highest velocity Vmax. Assume now that during the travelof the tank the player tries to turn the steering element 20A through adesired angle θ (in this example, 90 degrees). This steering angle θ isread by the CPU 101, which calculates a sight angle Ya through which thesight 33 is rotated in the steering direction of the steering element inunits of a small increment of the changing steering angle of the momentat the given velocity α (FIG. 6), using the expression (1). The sightangle Ya is handled as a target rotational angle Zo and a rotationalangle Za is calculated through which the tank body 32 is rotated followsthe sight 33. In addition, by handling the sight angle Ya as a targetrotational angle Zo, a rotational angle Za is calculated through whichthe tank body 32 is rotated while following up the sight 33. In thiscalculation, the rotational angle Za is calculated as an angle smallerby a coefficient "Kb·V" of the expression (2) than the sight angle Ya.In this case, since the traveling velocity V is high, and the value ofthe coefficient "Kb·V" is also large, and the rotational velocity of thetank body 32 controlled so as to be substantially the same as thepredetermined rotational velocity α of the sight 33, data on therotational angle Za of the tank body 32 is delayed slightly compared tothe sight angle Ya.

This situation is schematically shown as an example in FIGS. 11 (1)-(5).More specifically, as the time elapses from t11 to t15, the sight 33changes, for example, in order of 0 degrees (initially, time t11), 30degrees (time t12), 60 degrees (time t13), and 90 degrees (after timet14) in correspondence to the respective time-dependent phases of thesteering angle θ increasing until 90 degrees. In parallel with this, therotation (direction) of the vehicle body 32 also changes, for example,in order of 0 degrees (initially, time t11), 29 degrees (time t12), 58degrees (time t13), 87 degrees (time t14), 90 degrees (time t15). Thatis, when the tank 31 travels at increasing velocity, the tank body 32rotates while following up the sight angle substantially on a real timebasis and hence the quantity of delay is reduced. Especially, when thetank is the highest velocity V=Vmax, the tank body 32 rotates atsubstantially the same velocity as the sight 33.

As will be seen from the illustration of FIGS. 10 and 11, when thesteering element 20A of the control unit 20 is operated, and when thetraveling velocity V of the tank 31 is relatively low (for example, V=Vsin FIG. 6), the rotational velocity Vr of the vehicle body 32 is low.Thus, the vehicle body 32 follows up the rotation of the sight 33 in aconsiderably delayed manner. When the traveling velocity V of the tank31 is medium (for example, V=Vmd in FIG. 6), the rotational velocity Vrof the vehicle body 32 takes a medium value. Thus, the vehicle body 32rotates following the sight 33 with a medium delay, which decreases asthe tank 31 travels at increasing velocity. When V=Vmax, both rotates atsubstantially the same velocity, as shown in FIG. 11.

As described above, in response to the steering operation of thesteering element, both the sight 33 and the vehicle body 32 rotatethrough an angle depending on the steering angle θ. The vehicle body 32follows the sight 33 with a quantity of delay depending on the travelingvelocity V. The rotation of the sight 33 has priority, so that theplayer is only required to perform the steering operation by beingconscious of the rotational direction of the sight 33. Thus,manipulation of the two steering elements, the operation of which wasrequired conventionally, is not required now, so that control of thedirection of the objects is greatly simplified and the player has anincreased margin for enjoying the game. Since the number of steeringelements is reduced compared to the conventional system, cost reductionis achieved by reducing the number of components and the control unit ofthe game device is prevented from being large-scale or complicated.

Since in the present embodiment the sight 33 is controlledpreferentially in response to the steering operation, there is nohindrance to the game's operations on control of the sight 33 such as,for example, firing a bullet from a canon. Because of such preferentialcontrol, the steering angle, the position of the sight 33 and an image(that is, the visual field of a virtual camera) displayed on the monitor30 are always in phase with each other, which is convenient for the tankgame.

While the embodiment has been illustrated as the arcade video gamedevice, the direction control method and apparatus according to thepresent invention is also applicable advantageously to the home videogame devices. While in the conventional home game devices two directioncontrol elements, that is, the joy pad and steering element, have beenrequired to be provided and combined in manipulation, according to thepresent invention, only one direction control unit, for example, onekind of joy pad is required to be operated. Thus, operation is easy, andthe game device is simplified and reduced in size.

While in the embodiment the tank has been illustrated as the objectwhich requires control of a plurality of directions, the object need notnecessarily be limited to a tank. Other movable objects such as, forexample, battleships, fighters, etc., may be used, of course.

While in the embodiment the sight of the two direction control elements,that is, the vehicle body and sight, of the tank as the traveling objectis preferentially controlled and the vehicle body is controlled so as tofollow up the sight, the rotation of the vehicle body may be firstcontrolled and the sight may follow up the movement of the vehicle body.If the content of the battle game of the tank lays emphasis on thetravel of the vehicle body rather than the free use of the sight,control which realizes this concept can increase playability as the casemay be.

We claim:
 1. An object direction control method for displaying on amonitor an object having a plurality of direction control elements eachof which is controllable in a rotational direction, along with abackground in a moving state, comprising the steps of:designating atarget angle for the plurality of direction control elements;controlling a rotational angle of one of the plurality of directioncontrol elements on the basis of the target angle to turn the onedirection control element in a rotational direction; and controlling arotational angle of at least one other direction control element tofollow up the one direction control element by automatically turning theat least one other direction control element in the rotational directionof the one direction control element.
 2. An object direction controlmethod according to claim 1, wherein the number of direction controlelements is two.
 3. An object direction control method according toclaim 2, wherein the object comprises a war tank used in a tank game ofa game device, and the two direction control elements comprise a bodyand a sight of the tank.
 4. An object direction control method accordingto claim 3, wherein the one direction control element comprises thesight, and the at least one other direction control element comprisesthe body of the tank.
 5. An object direction control method according toclaim 1, wherein a velocity at which the one direction control elementis turned depends upon a moving velocity of the object.
 6. An objectdirection control method according to claim 5, wherein a new rotationalangle Ya of the one direction control element is given by

    Ya=Yb+Ka·θ

where θ is the target angle, Yb is a current rotational angle of the onedirection control element, and Ka is a constant.
 7. An object directioncontrol method according to claim 5, wherein the at least one otherdirection control element is turned depending on the moving velocity ofthe object and the rotational angle of the one direction controlelement.
 8. An object direction control method according to claim 7,wherein a new rotational angle Za of the at least one other directioncontrol element is given by

    Zo=Ya

    Za=Zb+Kb·V·(Zo-Zb)

where Zo is a target rotational angle of the at least one otherdirection control element, Ya is the rotational angle of the onedirection control element, Zb is a current rotational angle of the atleast one other direction control element, Kb is a constant, and V isthe moving velocity of the object.
 9. An object direction control methodaccording to claim 8, wherein the turning velocity of the one directioncontrol element is slightly higher than a maximum turning velocity ofthe at least one other direction control element.
 10. An objectdirection control method according to claim 1, wherein the step ofcontrolling the rotational angle of the at least one other directioncontrol element includes the substep ofcontrolling the rotational angleof the at least one other direction control element to automaticallyturn the at least one other direction control element in the rotationaldirection of the one direction control element with delay.
 11. An objectdirection control apparatus for displaying on a monitor an object havinga plurality of direction control elements each of which is controllablein a rotational direction, along with a background in a moving state,comprising:target angle designating means for designating a target anglefor the plurality of direction control elements; first direction controlmeans for controlling a rotational direction of one of the plurality ofdirection control elements on the basis of the target angle to turn theone direction control element in the rotational direction; and seconddirection control means for controlling a rotational direction of atleast one other direction control element to follow up the one directioncontrol element by automatically turning the at least one otherdirection control element in the rotational direction of the onedirection control element.
 12. An object direction control apparatusaccording to claim 11, wherein the number of the plurality of directioncontrol elements is 2, wherein the object is a war tank used in a tankgame in a game device, and wherein the two direction control elementscomprise a body and a sight of the tank.
 13. An object direction controlapparatus according to claim 12, wherein said target angle designatingmeans comprises a single direction input unit for manually inputtingdirection data on the target angle.
 14. An object direction controlapparatus according to claim 13, wherein the first direction controlmeans comprises means for rotating the one direction control element ata velocity in accordance with the target angle, and means forcalculating a new rotational angle Ya of the one direction controlelement, given by

    Ya=Yb+Ka·θ

where θ is the target angle, Yb is a current rotational angle of the onedirection control element, and Ka is a constant.
 15. An object directioncontrol apparatus according to claim 14, wherein the second directioncontrol means comprises means for rotating the at least one otherdirection control element in accordance with a moving velocity of theobject and the rotational angle of the one direction control element,and means for calculating a new rotational angle Za of the at least oneother direction control element by

    Zo=Ya

    Za=Zb+Kb·V·(Zo-Zb)

where Zo is a target rotational angle of the at least one otherdirection control element, Ya is the rotational angle of the onedirection control element, Zb is a current rotational angle of the atleast one other direction control element, Kb is a constant, and V isthe moving velocity of the object.
 16. An object direction controlmethod for displaying on a monitor an object having a plurality ofdirection control elements each of which is controllable in a rotationaldirection, along with a background in a moving state, comprising thesteps of:designating a target angle for the plurality of directioncontrol elements; controlling a rotational angle of one of the pluralityof direction control elements on the basis of the target angle to rotatethe one direction control element by a degree equal to the rotationalangle at a first velocity of rotation; and controlling a rotationalangle of at least one other direction control element to rotate the atleast one other direction control element by a degree corresponding tothe rotational angle of the one direction control element at a secondvelocity of rotation different than the first velocity of rotation. 17.An object direction control apparatus for displaying on a monitor anobject having a plurality of direction control elements each of which iscontrollable in a rotational direction, along with a background in amoving state, comprising:target angle designating means for designatinga target angle for the plurality of direction control elements; firstdirection control means for controlling the rotational direction of oneof the plurality of direction control elements on the basis of thetarget angle to rotate the one direction control element in therotational direction at a first velocity of rotation; and seconddirection control means for controlling the rotational direction of atleast one other direction control element to rotate the at least oneother direction control element in the rotational directioncorresponding to the rotational direction of the one direction controlelement at a second velocity of rotation different than the firstvelocity of rotation.